The FEX-M3 nerve gas grenade, a product of Czerka Arms, was a type of infantry grenade designed for hand deployment. It was filled with the deadly FEX-M3 nerve gas. As one of Czerka's various chemical load grenades, it contained a chemical payload. Around the onset of the Clone Wars, the Galactic Senate outlawed the production of FEX-M3 nerve gas grenades. Despite this ban, a Galactic Republic factory located on the planet Belgaroth secretly manufactured a substantial quantity of these grenades for the Confederacy of Independent Systems during the war. When the Republic received intelligence suggesting the factory's potential links to the enemy, a clone trooper team consisting of four men was sent to investigate. During this mission, three troopers were killed by a native droidbreaker creature. However, the surviving clone, Sergeant Marrt, successfully completed the mission. He destroyed the shipment, incinerated the factory, apprehended its leader, Tarin, and recovered crucial data records. These records were instrumental in exposing two treacherous senators within the Republic. By the time of the Galactic Civil War, the grenade had resurfaced, being utilized by both the Galactic Empire and the Alliance to Restore the Republic.
The FEX-M3 nerve gas grenade was a small hand-thrown infantry grenade that contained the deadly FEX-M3 nerve gas. This potent, rapidly acting yellow gas targeted the autonomic nervous system and brain stem of most species. This resulted in the shutdown of these systems and incapacitation of the victim. While inhalation was the primary method of exposure, making gas masks a form of partial defense, they were insufficient. The FEX-M3 nerve gas was also absorbed through the skin. Complete protection required a full enviro-suit. As a member of the "chemical load grenades" family, the FEX-M3 nerve gas grenade was manufactured by Czerka Arms. Czerka's trade agreements mandated clear labeling of its dangerous contents. The market price for each FEX-M3 nerve gas grenade was 1050 credits.
The grenade featured rounded contours, consisting of a cylindrical top section and a conical handle extending outwards, separated by a slightly indented middle section. At the top of the grenade was a circular indentation, and rectangular protrusions were visible on the sides. The top section and handle were light gray, while the middle section was a darker shade. Weighing only 0.5 kilograms, it had a maximum range of 20 meters when thrown, gripping the handle. A blaster shot could trigger the FEX-M3 nerve gas grenade. Upon detonation, the grenade released the FEX-M3 nerve gas as an aerosol within a limited radius. This gas cloud, though short-lived, was powerful enough to instantly kill a droidbreaker and was lethal to Humans. The grenade casing disintegrated upon detonation, making it impossible to refill and limiting it to single use.
The FEX-M3 nerve gas grenade's development occurred sometime before or during the early stages of the Clone Wars. Czerka Arms' factories handled both its production and filling. It became a common weapon among military forces, allowing for the elimination of enemy troops without structural damage. Consequently, its deadly nature led to a ban by the Galactic Senate. However, during the initial two years of the war—a year after the official ban—a Galactic Republic factory under Czerka's ownership, situated on Belgaroth, entered into an agreement with the InterGalactic Banking Clan. This clan was a member of the Confederacy of Independent Systems. Tarin, the factory's head, promised Reep Tonith, the Clan's representative, the production of 100,000 FEX-M3 nerve gas grenades for the Confederacy in return for a substantial financial reward.
Upon receiving information about Tarin's clandestine dealings with the Confederacy, the Republic deployed a scout team of four clone troopers, led by Sergeant Marrt, to conduct an investigation. The team advanced toward the factory, and Marrt ordered his men to remain hidden while he entered alone. Simultaneously, Tonith arrived to collect the shipment, only to discover that Tarin had not yet fulfilled the order. Tarin requested a twelve-hour extension to complete the required number of grenades, which Tonith reluctantly granted. Marrt overheard their exchange, then inspected the completed portion of the shipment and discovered the grenades. After taking a FEX-M3 nerve gas grenade as evidence, Marrt attempted to rejoin his squad undetected, but Tonith's battle droid escort spotted him. As battle droids began firing, Marrt and his team retreated into a swamp. Tarin allowed their escape, assuming they would be killed by the swamp's native droidbreaker creatures.
Convinced that the FEX-M3 nerve gas grenades would give the Confederacy a strategic advantage and doom the Republic's clone army, the four clone troopers attempted to contact the Republic, but were prevented by a dense fog in the swamp. At that moment, a droidbreaker attacked, killing the clone troopers one by one. Sergeant Marrt was the sole survivor. In a desperate attempt to defeat the droidbreaker, he climbed a tree and threw the FEX-M3 nerve gas grenade taken from the factory at the creature. The droidbreaker caught the grenade in its mouth, and Marrt fired his blaster pistol. A shot struck the grenade, causing it to detonate and release its FEX-M3 nerve gas, instantly killing the creature.
Driven to avenge his fallen comrades, Marrt returned to the factory, destroyed Tonith's droids, burned the facility, and destroyed the entire shipment of grenades, but not before recovering Czerka's data records. Despite sustaining serious injuries, Marrt captured Tarin, though Tonith escaped. The data records Marrt recovered exposed two Republic senators who had been profiting from deals with the Confederacy. Despite the ban on FEX-M3 nerve grenade production and the destruction of the Czerka facility, these grenades eventually became widely available again during the Galactic Empire's reign. They were used on battlefields by both sides of the Galactic Civil War: the Empire and the Alliance to Restore the Republic. The grenade continued to be used during the devastating Yuuzhan Vong War decades later.
The FEX-M3 nerve gas grenade was initially mentioned in the 1991 supplement for Star Wars Miniatures Battles, a tabletop wargame system by West End Games. The grenades were presented as a type of ordnance for use in the game. It remained unmentioned for years until the 2002 Arms & Equipment Guide, a supplement for Wizards of the Coast's Star Wars Roleplaying Game, listed it as a type of chemical load grenade. It was briefly mentioned in The New Essential Guide to Weapons and Technology, a 2004 reference book, before its first appearance in A Trooper's Tale, a short comic strip published in Star Wars: The Clone Wars Comic UK 6.8 in May of 2010. Robin Etherington wrote A Trooper's Tale, and Andres Ponce illustrated it.